MELBOURNE, Australia - Serena Williams lost at the Australian Open for the first time since 2008, struggling with her serve and hitting too many unforced errors in a 6-2, 6-3 loss to Ekaterina Makarova on Monday.

Williams was surprised by the power of the groundstrokes from the Russian left-hander, who at No. 56 was the lowest-ranked woman to make the fourth round of the season's first major.

The dominant force at Melbourne Park this century, Williams had lost only two matches at the Australian Open since winning the first of her five titles here in 2003. She was on a 17-match winning streak after capturing titles in 2009 and 2010 and missing last year due to injury.

"I don't know what to say. Amazing feeling and first time in quarterfinals," the 23-year-old Makarova said. Williams is "an unbelievable player. It's really tough to play against her so I'm really happy I finished it in my way."

Williams didn't blame her ankle injury or the heat, which increased to 93 during the day, but couldn't even describe how bad her serve was.

"Yeah, I served like .... it's inappropriate. I don't know," she said. "It was just disastrous really. Maybe I should have started serving lefty."

The absence of Williams opens up the women's draw, with Maria Sharapova, defending champion Kim Clijsters and Wimbledon winner Petra Kvitova the only major winners still in contention.

Kvitova had some trouble late before beating former top-ranked Ana Ivanovic 6-2, 7-6 (2) in the opening match Monday.

She'll next play Serra Errani of Italy, who beat 2008 semifinalist Zheng Jie 6-2, 6-1.

On the men's side, two-time Australian Open runner-up Andy Murray only spent 49 minutes on court and was leading 6-1, 6-1, 1-0 when Mikhail Kukushkin retired from their fourth-round match with a left hip injury, giving him an easy path into the quarterfinals.

He'll next play Kei Nishikori, who had a stunning 2-6, 6-2, 6-1, 3-6, 6-3 win over sixth-seeded Jo-Wilfried Tsonga, the 2008 finalist.

Defending champion Novak Djokovic was playing Lleyton Hewitt on Monday night.

On Sunday, Clijsters set up a quarterfinal against top-ranked Caroline Wozniacki, who had a 6-0, 7-5 win over former No. 1 Jelena Jankovic.

Third-seeded Victoria Azarenka advanced with a 6-2, 6-2 win over Iveta Benesova. She next plays eighth-seeded Agnieszka Radwanska.

Roger Federer more or less held a clinic at Rod Laver Arena, where he has won four of his 16 Grand Slam titles, on Sunday night - a 6-4, 6-2, 6-2 victory over Bernard Tomic that moved him into the quarterfinals for a 31st consecutive major.

Federer plays 2009 U.S. Open champion Juan Martin del Potro.

Rafael Nadal advanced with a convincing win over fellow Spaniard Feliciano Lopez.

He will play Tomas Berdych, hoping to avoid a third consecutive quarterfinal loss in Melbourne.